1. FIELD OF THE INVENTION
The invention relates to a commutator with an armored segment set arranged on a hub or anchor shaft with an insulating layer disposed therebetween, as well as to a method for the manufacture of such a commutator.
2. DESCRIPTION OF THE PRIOR ART
Known commutators having armored segment sets are of the arch-thrust type construction. With this construction so-called breaks, which sometimes occur at high revolutions, can be avoided, even under high centrifugal loads, because the arch-thrust pressure can be made so great that the surface compression between the segments and insulating layers arranged between adjacent segments is sufficient under any operating conditions to reliably prevent the segments from moving radially outwardly. Often, however, commutators are subjected not only to large centrifugal forces, but also to high thermal loads. The deformation of the brush contact surfaces that takes place as a result of the heating of the commutator which deformation is reversible and is in the form of short and/or long wave deviations from the cylindrical shape, thus limits the maximum rpm at which the commutator can be used. The previously employed methods for avoiding or minimizing the thermal deformation of the brush contact surface, particularly an increase in the arch-thrust, have brought no success.
The basic object of the invention is to create a commutator of the above described type, which has no or at least a significantly smaller heat deformation than the known commutators.
The solution according to the invention originates from the recognition that in commutators of the arch-thrust type, the radial forces emanating from the armored segment set resulting from the arch-thrust are of varying magnitudes because of the unavoidable material inhomogeneity and dimensional non-symmetry of the segment set over the circumference or length thereof. They cause balancing adjustments which are different for each commutator, with corresponding distortion of the segment set even during its manufacture. The deformation caused by the distortion of the segment set is indeed eliminated by machining on a lathe the finished commutator, but the varying magnitudes of the radial forces over the length of the segment set remains. A new deformation of the segment set and thereby of the brush contact surface is therefore preprogrammed and occurs under all types of operating loads as a result of the weak reaction forces of the armor elements, which are especially formed to endure centrifugal forces and to maintain a sufficient arch-thrust, but are much less resistant to bending.
Even as a result of the load from the centrifugal force, the radial forces existing over the length of the segment set in nonuniform magnitudes together with the radial components resulting from an unavoidable imbalance of the segment set, as a consequence of constant expansion of the segment set caused by increasing rpms, result in an increase in the differences in magnitude of the radial forces over the length of the segment set. The continuous heat-up of the commutator occuring during operation until operating temperature is reached causes a further increase of the difference in magnitude of the radial forces acting over the length of the segment set. This increase of the difference in the magnitude of the radial forces during heating occurs by superimposed forces caused by means of the heat-dependent arch-thrust increase and by means of the increasing asymmetry of the segment set resulting from the pressure and heat increase and from the inhomogeneity of the segment set, particularly of the insulating layers. In addition, there arises the fact that, because of the relatively soft, orthotropic segment set, the build-up or decrease in the radial forces acting over the length of the segment set and arising from changes in operating conditions takes place over a relatively long way. In other words, with the onset of centrifugal force and particularly heat-loading, the force balancing adjustment takes place over a correspondingly large expansion of the segment set, which thereby increasingly loses its original shape and orientation to the commutator hub and is at least still connected only with the commutator hub or the shaft, as a result of the deformation, by local, uncontrolled contact with the commutator hub.
In order to prevent these deformations in commutators of the arch-thrust construction, such commutators must thus have a high degree of material homogeneity and dimensional symmetry. The realization of the requirements necessary therefor, such as angle trueness and identical thickness of all segments, largely tolerance-free insulating layer thickness, homogeneous material and the most ideal possible axial and radial symmetry in the construction of the segment set during its manufacture and up to completion of the commutator, would, to the extent they would even be possible, result in high costs.